OTel stats are incorrect for block output notes

[Mirko-von-Leipzig]

Ah yeah nice catch. It looks like the block variant is incorrect now.

ProposedBlock::output_note_batches should be used there it seems, though the naming is a bit confusing :)

Originally posted by @Mirko-von-Leipzig in #783 (comment)

[Mirko-von-Leipzig]

Given this is a relatively tiny fix, it might be good to combine this with #725 and add a test demonstrating this "fix".